The Hilltop House was originally designed by architect Thornton Ladd in 1953 and was reworked by Marmol Radziner.

From the site:

Located in Pasadena, California, the Hilltop House and Studio were originally designed by architect Thornton Ladd in 1953. Spread over five acres, the mountaintop retreat is comprised of a 6,700 square foot house and a 1,300 square foot detached studio. The resident of the studio converted the space into a modern guest house. Ladd’s original design integrated indoor and outdoor spaces and took advantage of the dramatic views. The owner’s interest in Japanese architecture and design informed the choice of interior materials – warm woods including cedar and maple for the floors and ceilings, furnished with tatami mats.